import tkinter as tk


window = tk.Tk()
window.title('my window')
window.geometry('200x100')


var = tk.StringVar()

l = tk.Label(window,
             textvariable=var,
             bg='green',
             font=('Afrial', 12),
             width=15,
             height=2)
l.pack()

on_hit = False

def hit_me():
    global on_hit
    if on_hit == False:
        on_hit = True
        var.set('you hit me')
        
    else:
        on_hit = False
        var.set('')
        
    
b = tk.Button(window, text='hit me',width=15, height=2,
              command=hit_me)

b.pack()


window.mainloop()
